A bit is a binary digit, with a value of 0 or 1. Popcount counts the number of 1-bits; and, as said, population count actually is the canonical name. You can a

A bit is a binary digit, with a value of 0 or 1. Popcount counts the number of 1-bits; and, as said, population count actually is the canonical name. You can apply __builtin_popcount in a loop if you want to count bits in multiple words. The point of exposing this particular operation for an unsigned int is that a recent CPU will likely have an efficient operation for it. Operating on larger units is something better left to your own code or a library. You're definitely not "back to square 1", because the intrinsic offers you an operation that would otherwise only be accessible with inline assembly.